Method and apparatus for filling a pulp tower

ABSTRACT

Pulp is effectively and simply fed into a pulp tower using at least one feed pipe having a number of openings that are spaced different distances from the bottom of the pulp tower. The opening through which the pulp being fed into the tower flows automatically changes depending on the level of the existing pulp in the tower. The feed pipe may have a wide variety of different configurations with openings formed or shaped in different manners, and baffles or similar guides can be used to uniformly spread the pulp being fed through the feed pipe onto the top surface of the existing pulp without mixing. This configuration allows the amount of pulp pumping energy to be minimized while still effectively feeding pulp into a tower.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national phase of PCT ApplicationPCT/F197/00233, filed Apr. 15, 1997.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for filling apulp tower. The invention is especially well applicable in the woodprocessing industry to filling high consistency pulp towers andcorresponding storage towers containing fiber suspension.

Pulp towers used in the wood processing industry are, as know, mostcommonly tanks containing high-consistency pulp, the consistency being10-20%, although pulp at a lower consistency is also used occasionally.These tanks are used for example for storing pulp or as blow tanks ofsome apparatus, i.e. for example for storing pulp which comes in batchesfrom batch digesters, the pulp being then used as a uniform flow in thesubsequent treatment apparatus. In other words, it is characteristic oftowers according to the invention that the level thereof varies to agreat extent, although they most commonly have an optimum level, and theintention is to keep the surface of the pulp at this level.

Several different arrangements for filling pulp towers of theabove-mentioned type are known from the prior art. One of the oldestmethods known is pumping the pulp to the top of the tower, wherefrom itis allowed to drop down more or less directly. If the pulp is allowed todrop directly onto the pulp below, it goes without saying that the pulpdropping from high above permeates the surface of the pulp in the towerand penetrates deep down into the old pulp. There are several drawbacksto this. For the first, if a dilution of the pulp is performed in thelower portion of the tower, as is very often the case, the pulp fed tothe tower may permeate as far as to the dilution zone. This results inthe pulp discharging uncontrollably to the dilution zone and thedilution not being as uniform as would be required for the apparatusfollowing the tower. Another problem is that the pulp, when permeatinginto the old pulp, is drifted closer to the discharge opening of thetower than the pulp already present in the tower, whereby the content ofthe tower does not change uniformly, but part of the pulp passes out ofthe tower within some minutes, whereas another part may have to stay inthe tower even as long as several weeks. This, in turn, brings aboutmore problems. For the first, it is impossible to even imagine that pulpstaying in a tower for days or even weeks could be of the same qualityas fresh pulp. For the second, a complete change of stock in towers likethis may take days and at least several hours, the pulp discharged fromthe tower being thus a mixture of old and new pulp of this time span.Depending on the following object of use of the pulp, this "intermediatepulp" may in the worst case be totally unusable. Furthermore, the oldpulp staying longer in the tower and the new pulp permeating deeper intothe tower, liquid is gradually filtered from the surface of the pulplayer, whereby the surface layer hardens and gets thus damaged moreeasily. Finally, energy consumption may also be mentioned as a problem,at least from the point of view of our invention, since pumping thewhole production volume of a pulp mill, i.e. about 1,000 tons of pulpper day, to the height of 20-30 meters, only to be dropped down to theheight of about 3-10 meters, can be regarded as wasting of pumpingenergy. In other words, the pumping energy that would be really neededis most often less than half of the energy now used.

It is of course possible (U.S. Pat. No. 3,964,962) to discharge the pulponto a distributing device, for example onto a rotating plate arrangedin the upper portion of the tower, by means of which plate the pulp isdistributed more uniformly all over the cross-section of the tower. Partof said problems may be solved in this way, but pumping energy is stillconsumed to the same extent as before, and in addition, the arrangementof distributing devices of pulp in the upper portion of the towerresults in both complicated structures and great energy consumption. Asthe distributing device decomposes the pulp flow into drops, or at leastinto relatively small particles, a significant amount of air is bound tothe pulp during the down-drop, which air will have to be removed atlater states of the process by means of vacuum pumps consuming a greatdeal of energy, or by means of corresponding arrangements.

In connection with some towers, it has been taken into account that thetower is rarely full, and therefore the energy consumption may bedecreased by leading the feed pipe of the pulp from the side of thetower into the inside thereof. If the feed pipe is above the pulpsurface, the pulp being supplied through the supply opening penetratesthrough the surface of the pulp layer in the tower into the pulp columnat least within some distance, whereby the same problems with pulps ofdifferent ages still exist even if they are not as difficult as in thetowers filled from the top.

The next alternative is to dispose the feed pipe on the side of thetower below the pulp surface, though directed in such a way that thepulp is supplied substantially onto the pulp layer in the tower. Thisarrangement works exactly as long as the surface level in the towerremains unchanged. If the surface level varies several meters, theproblem may be, for example, that the pulp fed into the tower remainsseveral meters below the pulp surface, whereby the pulp on the surfacelevel cannot discharge, and the new pulp being fed passes first to thedischarge. Correspondingly, if the surface level drops a lot below thefeed opening, the pulp being fed into the tower penetrates deep into thepulp layer, causing the very problems described above. In other words,this method of feeding is suitable for such cases only where the surfacelevel of the tower remains relatively stable.

Another problem relating to the filling of pulp towers emerges inconnection with batch cooking processes, and in particular with thefilling of the blow towers thereof. It is generally known that whenemptying a batch digester, the consistency of the pulp being dischargedfrom the digester varies to a great extent. Hereby, areas of pulp havingdifferent consistencies are formed also in the blow tower, no matter bywhich prior art method it is filled, and this leads in most cases tovariation in the consistency of the pulp directed to the process stagefollowing the tower. This, in turn, causes various problems in brownstock washing, for example. As known, for example washers aredimensioned for an optimum consistency and deviating from thisinevitably weakens the operation result.

Various problems caused by the prior art arrangements described abovecan be solved by means of the method and apparatus of our invention, thecharacteristic features of which become apparent from the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described in more detail withreference to the appended figures, of which

FIG. 1 illustrates an apparatus in accordance with a preferredembodiment of the invention in two different applications;

FIG. 2 illustrates an apparatus in accordance with a second preferredembodiment of the invention in two different applications;

FIG. 3 illustrates an apparatus in accordance with a third preferredembodiment of the invention in two different applications; and

FIGS. 4a-c illustrate details in accordance with some other preferredembodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In accordance with FIG. 1, the apparatus according to the inventioncomprises a substantially vertical feed pipe 12 arranged centrallywithin a pulp tower 10 through the bottom thereof. The feed pipe 12extends preferably at least to such a height in the tower in which thepulp level varies under normal conditions. In other words, the upper endof the pipe 12 is located in the tower somewhat above the upper limit ofthe variation span of the normal surface level. In the embodiment ofFIG. 1, the pipe 12 is formed by portions 14, 16 and 18, the diametersof which enlarge upward. At the attachment point of the portions, pulpsupply openings 20 are arranged which open either, as illustrated in thefigure, to the side, directed by baffles 22 arranged at the upper partsof the narrower pipe portions, respectively, or directly downwardwithout said baffle.

The apparatus functions in such a way that when pulp is pumped into thetower 10 through the feed pipe 12, the pulp already in the tower 10clogs supply openings 20, so that the new pulp flows in the feed pipeupward past the openings (the right-hand side of FIG. 1), until itdischarges either through the first unclogged supply opening, or to bemore precise, through the first opening through which the flowresistance is insignificant enough for the kinetic energy of the pulp toovercome the resistance, or from the upper end of the pipe onto thesurface of the pulp already in the tower 10. The spacing between thesupply openings 20 in the feed pipe 12 are preferably adjusted such thatthe pulp discharging from the openings 20 does not have time to generatea significant downward velocity component which would promote thepenetration of the pulp deep into the "old" pulp. Preferably, thespacings between the supply openings 20 in the vertical direction are inthe order of 1-2 meters, the surface area being in the order of (0.5-2) * the diameter of the feed pipe. One preferable way to dispose thesupply openings is to arrange them as squares standing on their cornersand to position them alternatingly around the pipe, so that, practicallyspeaking, one or more openigs are all the time at the point of the freepulp level. Corresponding positioning may also be effected by means ofopenings of other shapes, for example by rectangular or round openingsor openings with curved edges. The diameter of the feed pipe 12 isdetermined according to the capacity of the tower, varying inconventional towers preferably most often between 0.5-1 meter. Theleft-hand side of FIG. 1 illustrates a case in wich the surface of thepulp in the tower 10 is relatively low, whereby the pulp discharges ontothe pulp surface from the supply opening 20 disposed lower in the pipe12, preferably in such a way that due to the effect of the baffle 22 itforms a shape of a fan in the direction of the pulp surface in thetower. In the bottom portion 24 of the tower 10, a dilution zone of thepulp, which is most often located just there, is shown with a mixer 26and a discharge opening 28 thereof. The tower 10 may also be providedwith other types of dilution and/or discharge apparatus which may alsobe arranged in another way without affecting the operation of theinvention.

FIG. 2 illustrates an apparatus according to a second preferredembodiment according to the invention, which apparatus has been modifiedto be used with a bottom pillar, the use and operation of which isdescribed in more detail in FI patent application 94709. In theembodiment of FIG. 2, the pulp is introduced into the tower 10 from aside wall 102 of the bottom portion 124 thereof (most commonly fromeither a conic or cylindric part), although in connection with ourinvention the pulp may as well be introduced through the lower end of abottom pillar 104. Now, however, the feed pipe 112 for the pulp mayserve as one of the supporting structures of the bottom pillar 104, ifit is considered that supporting structures are required. In theembodiment of the figure, a feed pipe 112 bends at the point of theextension of the bottom pillar 104 in the vertical direction and extendsupward within a pipe 114 having a larger diameter and extending upwardat the upper end of the bottom pillar 104. The feed pipe 112 extends inthis embodiment close to the larger pipe 114, which is, relative to thelevel of the tower, located preferably at the same height as the upperend of the feed pipe 12 illustrated in FIG. 1, in other words at thesame height as the upper end of the largest part of the pipe 12.

The apparatus according to FIG. 2 operates in such a way that when thepulp surface is high (the right-hand side of the figure), the pulp beingfed passes from the upper end of the feed pipe 112 into the larger pipe114 and further from the upper end thereof onto the pulp layer in thetower 10. When, on the other hand, the surface is lower (the left-handside of the figure), the pulp passes from the feed pipe 112 into anannular space 116 between the feed pipe 112 and the larger pipe 114 andtherefrom through a supply opening/openings 120 onto the pulp layer inthe tower. In this embodiment, too, there are baffles 122 in connectionwith the supply openings 120, by which baffles the pulp is discharged inthe substantially radial horizontal direction onto the pulp layer.

The above-described feeding method is especially advantageous when achange of stock is performed in the tower, in which case it is essentialto be able to discharge the former stock from the tower in such a waythat as little of it as possible is mixed with the new stock. By meansof the method according to our invention the change of stock takes placesimply in such a way that the pulp level in the tower is moved to a lowposition, somewhat below the supply openings 120, as illustrated by theleft-hand side of FIG. 2. When beginning to feed new stock to the tower10, it is possible to take advantage of the difference in height betweenthe feed pipe 112 and the supply openings 120 as well as of the baffles122 of the supply openings in such a way that the pulp being suppliedfrom the feed pipe 112 into the space 116 has a relatively great flowvelocity in the space 116 when being dropped from the level of the upperend of the feed pipe 112 to supply openings 120, whereby it is suppliedthrough the openings 120 directed by the baffles 122 at rather a greathorizontally directed velocity onto the surface of the pulp in the tower10. Thus, when changing the stock, the new pulp coming to the tower 10is settled as a uniform layer on the old stock, which means that thetime spent on the change of stock may in the best case be calculated inminutes and not in hours, days, or even weeks, as in connection withprior art pulp towers. Also in FIG. 2, a dilution zone usually locatedin the bottom portion 124 is shown therein with a mixer 26 and adischarge opening 28. However, the tower 10 may be provided with othertypes of dilution and/or discharge apparatus which may be arranged inanother way without affecting the operation of the invention.

Furthermore, it is worth mentioning about the pipes used that instead ofbeing composed of several pipes having different diameters, the feedpipe 12 may in the embodiment of FIG. 1 also be a cone enlarging upward,on the wall of which the supply openings are arranged. Correspondingly,the feed pipe 112 in FIG. 2 could be a cone enlarging upward, whichwould mean that while the larger pipe is cylindrical, the space 116between the pipes would be an annular space enlarging downward. By thismethod it could be ensured that the pipes will not clog even if thepulps used are difficult to handle.

As regards the saving in energy consumption achieved by using theapparatus according to the invention, this may be optimized bycontrolling the lift height of the pump arranged in connection with feedpipes 12, 112 according to the level of the tower 10. In practice, thismeans chiefly the controlling of the rotation velocity of the pump.

It is yet to be noted that in some cases the feed pipe may be led intothe tower also through the roof thereof, for example when dischargingthe pulp into a storage tower from a bleaching tower having anupward-directed flow without an intermediate pumping (by the pressure ofthe feed pump of the bleaching tower), for example, but in such a casegood care has to be taken that the pulp discharge from the feed pipewill not penetrate deep into the old pulp. This may be ensured by anarrangement according to FIG. 3, for example, showing that the roof 210of the tower 10 is provided in this embodiment with a central pulp feedpipe 212 extending to some distance from the bottom of the tower, whichbottom is provided with a bottom plate 213. In the embodiment of thefigure, the bottom plate 213 is arranged in connection with a bottompillar 204, but in practice it may as well be supported by other means.From the same bottom plate 213, a pipe 214 extends concentrically withthe feed pipe 212. The pipe 214 has a larger diameter and is providedwith supply openings 220 all the way up the pipe 214. The operatingprinciple is as in connection with the previous embodiments. In otherwords, the pulp is fed to the tower 10 through the feed pipe 212. Thepulp bumps against the bottom plate 213, changes its direction, beginsto flow upward within the larger pipe 214 and discharges through thefirst openings that are unclogged, or through the first openings atwhich the flow resistance is so low that the kinetic energy of the pulpis sufficient to overcome it.

Another way to effect the filling of a pulp tank is to arrange a movablebottom in the feed pipe, which bottom moves according to the pulp levelsurrounding the feed pipe, so that the supply opening positioned closestto and above the bottom is at least at the same level as the pulpsurface, whereby the pulp flow discharging through the opening alwaysends up upon the pulp layer already in the tower.

FIGS. 4a and 4b illustrate a feed pipe in accordance with a preferredembodiment of the invention, or actually a feed pipe applicable tosolving two in a way opposite problems. By only minor changes the feedpipe may be modified to solve one problem or the other. A feed pipe 312illustrated in FIG. 4a is used in the manner already described inconnection with FIG. 1. In other words, when feeding pulp from belowinto the feed pipe, the pulp begins to discharge from the pipe into thetower through the first unclogged supply opening 320, or from the supplyopening having a sufficiently low flow resistance. In practice, the pulphereby ends up substantially upon the pulp already present in the tower.

In the case illustrated by FIG. 4b, a feed pipe 412 is as in FIG. 4a,except that in the embodiment of FIG. 4b the upper end of the feed pipe412 is closed by a cover 430 preventing the discharge of pulp throughthe upper end of the pipe. By means of this application it is possibleto solve the above-described problem, i.e. the generation of areas withdifferent consistencies in the blow tower of a batch digester. Thesolution is to mix the pulp already at the filling stage of the blowtower. This works in such a way that as the discharge of the pulpthrough the upper end of the feed pipe 412 is prevented, the pulpdischarges into the tower at several different levels through supplyopenings 420, whereby the tower is filled practically speakinguniformly. Naturally, the uniformity of the filling may be improved inmany ways. One alternative is to decrease the size of the feed pipeopenings toward the upper end of the pipe. In other words, by decreasingthe size of the openings, flow resistance is generated at the pointswhere it would otherwise be lower due to the proximity of the pulplevel. Another way is to arrange a movable cover system in the feed pipe412, in which the cover moves according to the rise of the pulp leveleither directly or with a delay (the cover being lower than the pulplevel). The above-mentioned alternatives may of course be combined, inother words supply openings of changing sizes may be used together witha movable cover in the same feed pipe. The closer the method used is tosuch a combination, the closer one gets to an optimum situation, wherethere would be a uniform supply of pulp into the pulp already in thetower, extending through the whole height of the pulp layer.

FIG. 4c illustrates yet another alternative for filling the blow towerfollowing a batch digester. In this embodiment a feed pipe 512 issubstantially similar to the pipe in FIG. 1. In other words, the feedpipe 512 is formed by portions 513-518 having different diameters. Theonly difference is that the pipe 512 narrows upward. In other words,each opening 520 at the point of the change in diameter cuts part of thepulp being fed into the tower and a baffle 522 disposed above theopening 520 directs the coming pulp flow to the side to be mixed intothe pulp already present in the tower.

Should the blow tower of a batch digester be of a type which is filledfrom above, all the arrangements according to the embodimentsillustrated in FIGS. 4a, 4b and 4c may be applied in the mannerpresented already in previous embodiments. For said reason, among otherthings, FIGS. 4a,4b and 4c are provided with both reference numerals, inother words the reference numeral ending in -12 denoting a case wherethe pipe is a so called feed pipe, and the numeral ending in -14denoting a case where the pipe is a so called larger pipe. In FIG. 4c,for example, the illustrated embodiment may be modified for feed takingplace from above in such a way that the lower end of the pipe portion514 is closed by a plate, which can rest for example upon a bottompillar in the manner illustrated in FIG. 3. Hereby, the pulp isintroduced from above, for example through a pipe portion 518, whichwould in this case extend close to the bottom plate, and is dischargedagainst the bottom plate turning the pulp flow upward, after which theoperation continues as described above.

As becomes obvious from the above description, a new method andapparatus for filling pulp towers has been provided, by which method thedrawbacks of the prior art apparatus and methods can be avoided.However, only a few preferred embodiments of the invention have beenpresented above, and the intention is not to reduce the scope of theinvention but to interpret it according to what is presented in theappended claims. Thus, it is for example possible to arrange more thanone feed pipe in the tower, if desired, for example in the mannerdescribed in FI patent 94442 and using a distributing device describedabove, whereby it can be ensured that the pulp is distributed uniformlyall through the cross-section of the tower. Furthermore, it has to benoted that the shape of the tower does not, by all means, have to be asdescribed in the appended figures, i.e. a tower having a cylindricbottom portion narrowed by a conic intermediate part, but it may as wellbe totally cylindric and provided with either an even or inclinedbottom, or a conic or semispherical bottom portion. In other words, thefilling method according to the invention is applicable to fillingtowers of any shape.

What is claimed is:
 1. A method of filling a substantially vertical pulptower having a bottom and side wall, using at least one feed pipe havinga plurality of openings spaced different distances from the bottom ofthe tower, said method comprising:(a) feeding pulp into the feed pipe sothat the pulp flows into the tower through the first opening from thebottom through which the flow resistance caused by pulp existing in thetower is insignificant enough for the kinetic energy of the pulp toovercome the flow resistance, the opening through which the pulp beingfed flows automatically changing depending upon the level of existingpulp in the tower.
 2. A method as recited in claim 1 wherein (a) ispracticed by uniformly feeding the pulp through the at least one feedpipe so that the pulp uniformly flows on top of the existing pulp in thetower.
 3. A method as recited in claim 1 wherein pulp existing in thetower has a top surface; and wherein (a) is practiced by spreading thepulp uniformly onto the surface of the existing pulp substantiallywithout mixing of the pulp being spread with the existing pulp.
 4. Amethod as recited in claim 1 wherein (a) is practiced by pumping thepulp into the at least one feed pipe to flow upwardly in the feed pipe;and further comprising (b) adjusting the pumping energy for pumping thepulp into the at least one feed pipe dependent upon the opening throughwhich the pulp flow from the at least feed pipe into the tower tominimize the amount of energy necessary for pumping.
 5. A pulp towercomprising:a bottom and a side wall, defining a tower interior; a pulpdischarge apparatus adjacent said bottom; at least one substantiallystationary feed pipe having at least a first portion thereof extendingat least partially vertically in said tower interior upwardly away fromsaid bottom; and said at least one substantially stationary feed pipefirst portion having a plurality of openings therein which allow flow ofpulp from the feed pipe into said tower interior, said openings spaceddifferent distances from said bottom so that said openings are atdifferent heights within said tower interior.
 6. A pulp tower as recitedin claim 5 wherein said at least one feed pipe comprises a first feedpipe having a first diameter and a second feed pipe substantiallyconcentric with said first feed pipe and having a second diameter largerthan said first diameter, and wherein said second feed pipe has saidplurality of different height openings and said first feed pipe has asingle height opening.
 7. A pulp tower as recited in claim 6 whereinsaid first feed pipe extending downwardly into said second feed pipe anddischarges pulp downwardly into said second feed pipe.
 8. A pulp toweras recited in claim 6 wherein said first feed pipe extends upwardly intosaid second feed pipe, and pulp flows from a top portion of said firstfeed pipe into said second feed pipe.
 9. A pulp tower as recited inclaim 5 wherein said feed pipe has a side wall and a top, and whereinsaid plurality of openings includes at least one opening in said sidewall of said feed pipe, and an open top of said feed pipe.
 10. A pulptower as recited in claim 5 further comprising at least one guideassociated with at least one of said feed pipe openings for guiding theflow of pulp through said opening into said tower interior in asubstantially horizontal direction.
 11. A pulp tower as recited in claim10 wherein said at least one guide is located below a feed pipe openingwith which it is associated.
 12. A pulp tower as recited in claim 10wherein said guide comprises a baffle.
 13. A pulp tower as recited inclaim 10 wherein said at least one guide is located above a feed pipeopening with which it is associated.
 14. A pulp tower as recited inclaim 5 wherein said at least one feed pipe comprises a single feed pipesubstantially concentric with said tower interior.
 15. A pulp tower asrecited in claim 14 wherein said feed pipe has at least two differentdiameter portions with a transition therebetween, and wherein one ofsaid openings is provided at each transition.
 16. A pulp tower asrecited in claim 15 wherein said different diameter portions areconsecutively larger the further said portions are spaced from saidtower bottom.
 17. A pulp tower as recited in claim 15 wherein saiddifferent diameter portions are consecutively smaller the further saidportions are spaced from said tower bottom.
 18. A pulp tower as recitedin claim 5 wherein said at least one feed pipe comprises a side wall;and wherein at least some of said openings are provided in said sidewall.
 19. A pulp tower as recited in claim 18 wherein said openings aresubstantially diamond shaped and provided in a plurality ofsubstantially vertically spaced rows with a plurality of openings ineach row.
 20. Apparatus for supplying pulp to a pulp tower, the pulptower having a bottom and a side wall, defining a tower interior; saidapparatus comprising:at least one substantially stationary feed pipehaving at least a first portion thereof extending at least partiallyvertically in said tower interior upwardly away from the tower bottom;and said at least one substantially stationary feed pipe first portionhaving a plurality of openings therein which allow flow of pulp from thefeed pipe into the tower interior, said openings spaced differentdistances from the tower bottom so that said openings are at differentheights within the tower interior.
 21. Apparatus for supplying pulp to apulp tower as recited in claim 20 wherein said at least one feed pipecomprises a first feed pipe having a first diameter and a second feedpipe substantially concentric with said first feed pipe and having asecond diameter larger than said first diameter, and wherein said secondfeed pipe has said plurality of different height openings and said firstfeed pipe has a single height opening.
 22. Apparatus for supplying pulpto a pulp tower as recited in claim 20 wherein said feed pipe has a sidewall and a top, and wherein said plurality of openings includes at leastone opening in said side wall of said feed pipe, and an open top of saidfeed pipe.
 23. Apparatus for supplying pulp to a pulp tower as recitedin claim 20 further comprising at least one guide associated with atleast one of said feed pipe openings for guiding the flow of pulpthrough said opening into the tower interior in a substantiallyhorizontal direction.
 24. Apparatus for supplying pulp to a pulp toweras recited in claim 20 wherein said at least one feed pipe comprises asingle feed pipe substantially concentric with said tower interior. 25.Apparatus for supplying pulp to a pulp tower as recited in claim 24wherein said feed pipe has at least two different diameter portions witha transition therebetween, and wherein one of said openings is providedat each transition.
 26. Apparatus for supplying pulp to a pulp tower asrecited in claim 20 wherein said at least one feed pipe comprises a sidewall and wherein at least some of said openings are provided in saidside wall and are substantially circular or substantially diamondshaped.